We have been investigating nucleic acid structure involved in the control of transcription initiation and termination as well as in translational expression of various RNAs. Using recombinant DNA techniques we have been able to examine the relationship between regulatory function and DNA sequence in a variety of cellular and viral operon control regions. The characterization of mutants which affect both transcriptional and translational expression in these regions has afforded information on precise molecular events which lead to control element function. We have used a variety of defined prokaryotic genes to examine the requirements for translation in both eukaryotic cells and cell-free systems. Recombinant DNA techniques have been used to develop plasmid, phage and bacterial vector systems which allow the isolation, characterization, and comparison of prokaryotic transcriptional regulatory signals. This system has been adapted to allow efficient expression of a variety of prokaryotic and eukaryotic gene products in E. coli. Efficient expression of the E. coli galactokinase gene attached to a mammalian virus vector has been obtained within mammalian cells. This vector has allowed us to study transcriptional regulatory elements which function in eukaryotic cells.